T-cell subsets in delayed-type hypersensitivity, protection, and granuloma formation in primary and secondary Listeria infection in mice: superior role of Lyt-2+ cells in acquired immunity.

Immunity to Listeria monocytogenes was studied in mice treated with rat monoclonal antibodies (MAbs) specific for the Thy-1.2, L3T4, and Lyt-2 T-cell markers. Three characteristic T-cell-mediated phenomena were investigated. Delayed-type hypersensitivity (DTH) to listerial antigen was totally abolished in mice treated with anti-Thy-1.2 or anti-L3T4 MAbs, whereas anti-Lyt-2 MAb treatment had no effect, regardless of whether the MAb was given during the induction or the expression of DTH. On the other hand, the elimination of bacteria from the spleens of infected animals was inhibited only by the application of either anti-Thy-1.2 MAb or anti-Lyt-2 MAb. This could be shown most impressively during the secondary infection of immune mice with a normally lethal dose of listeriae. In this situation, treatment with anti-Lyt-2 MAb sufficed to completely abolish immunologic memory, whereas anti-L3T4 MAb had only a marginal effect on antibacterial protection. However, the accelerated development of mononuclear cell foci in the livers of immune mice was inhibited by the application of both anti-L3T4 MAb and anti-Lyt-2 MAb. It is concluded that in murine listeriosis, DTH and acquired immunity to reinfection are dissociable phenomena. Although DTH is a function of L3T4+ T lymphocytes, Lyt-2+ T cells are necessary and sufficient for the expression of acquired resistance to L. monocytogenes. The roles of the different T-cell subsets in granuloma formation warrant further investigation.